Gerald R. McDermott 
God’s Rivals [PDF ebook] 
Why Has God Allowed Different Religions? Insights from the Bible and the Early Church

In the providence of God, why are there other religions? Was the God of the Bible wise in allowing for them? Can they serve any purpose? Gerald R. Mc Dermott explores reflection on teaching from the Old and New Testaments and from a number of key teachers from the early church to suggest an answer to this perplexing but intriguing question. In the end Mc Dermott provides considerable insight into the troubling clash of world religions and offers a helpful Christian response.